The present invention relates generally to very low density polyolefins and films produced from very low density polyolefins. More specifically, the present invention is directed to very low density polyethylenes produced using metallocene catalysts, and cast extrusion films formed of metallocene-very low density polyethylenes having improved sealing and mechanical properties relative to conventional low density polyethylene films.
A variety of polymeric materials have been used successfully in thin cast films. A typical film casting process includes the steps of polymer extrusion, melt feeding through a slot die, melt draw-down in the air gap, chill-roll casting, edge-trim slitting, surface treating if necessary, and winding. The polyolefin film can be extruded onto a substrate of paper, metal foil, or other flexible substrate material to form an extrusion coated substrate. Extrusion of multiple layers of polymeric materials, including polyolefins as well as other materials, a process sometimes termed xe2x80x9ccoextrusionxe2x80x9d, is also well known.
A variety of polymerization processes have been used to make polyolefins, including polyethylene and polypropylene, suitable for extrusion coating applications. Such processes include gas-phase polymerization, solution polymerization and bulk polymerization. More specifically, gas phase polymerization processes using Ziegler-Natta or vanadium-based catalyst systems have been used to make xe2x80x9clow density polyethylenesxe2x80x9d (xe2x80x9cLDPEsxe2x80x9d), i.e., polyethylenes having densities of from 0.916 to 0.928 g/cm3; xe2x80x9cmedium density polyethylenesxe2x80x9d (xe2x80x9cMDPEsxe2x80x9d), i.e., polyethylenes having densities of from 0.929 to 0.940 g/cm3; and xe2x80x9chigh density polyethylenesxe2x80x9d (xe2x80x9cHDPEsxe2x80x9d), i.e., polyethylenes having densities greater than 0.940.
The low density polyethylene extrusion coating market is dominated by conventional LDPE made in a high-pressure process. LDPE is generally preferred because it is easy to extrude, has high melt strength thereby minimizing neck-in, and has good sealing characteristics. Linear low density polyethylene (xe2x80x9cLLDPExe2x80x9d) offers improved coating toughness, but its relatively narrow molecular weight distribution makes it more difficult to extrude, and it has relatively poor sealing properties; LLDPE makes up about 5% of the low density polyethylene extrusion market.
Although LDPE and LLDPE are widely used, these materials suffer from several disadvantages in extrusion coating applications. In applications requiring adhesion of a coating to polypropylene, LDPE and LLDPE offer relatively poor adhesion, thus necessitating the extra expense and complexity of an adhesive or tic layer. It would thus be desirable to have a polyethylene-based extrusion coating material capable of improved adhesion to polypropylene substrates. In addition, it would be desirable to have an extrusion coating material offering improved mechanical properties and improved sealing performance. Further, it would be desirable to have an extrusion coating material capable of being formed in thinner layer than is conventionally possible with LDPE and LLDPE. Still farther, it would be desirable to have an extrusion coating material providing better organoleptic properties than LLDPE.
U.S. Pat. No. 5,382,631 discloses linear interpolymer blends made from components having narrow molecular weight distribution (e.g. Mw/Mnxe2x89xa63) and a narrow composition distribution (e.g. CDBI greater than 50%/). The blends have either Mw/Mn greater than 3 and/or CDBI less than 50%, and combinations of each, and can be bimodal with respect to either or both molecular weight and/or comonomer content. The blends are generally free of blend components having both a higher average molecular weight and a lower average comonomer content than another blend component.
In one embodiment, the present invention is directed to a polymer blend, the blend including a very low density polyethylene (VLDPE) polymer having a density of less than 0.916 g/cm3, and a low density polyethylene (LDPE) polymer, having a density of from 0.916 to 0.940 g/cm3. Preferably the VLDPE and LDPE polymers are metallocene-catalyzed polymers.
In another embodiment, the present invention provides a polymer blend suitable for use as a film or a coating, the polymer blend including from 1 to 99% by weight of a metallocene-produced VLDPE polymer having a density less than 0.916 g/cm3, and from 1 to 99% by weight of an LDPE polymer having a density of from 0.916 to 0.928 g/cm3 wherein the sum of VLDPE and the LDPF is 100%. Alternatively, the blend can have from 5 to 95%, from 10 to 90%, or from 15 to 85% by weight of the LDPE polymer. The VLDPE polymer can have a melt index of from 6 to 15 dg/min, or from 9 to 12 dg/min. The VLDPE polymer can be an ethylene homopolymer, or a copolymer of ethylene and a C3 to C12 alpha-olefin. The LDPE polymer can have a melt index of from 0.5 to 15 dg/min, or from 1 to 10 dg/min. The LDPE polymer can be an ethylene homopolymer, or a copolymer of ethylene and a C3 to C12 alpha-olefin.
In another embodiment, the present invention is directed to a polymer blend, the blend including a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and at least one C3 to C12 alpha olefin and having a density of from 0.900 to 0.915 g/cm3 and a melt index of from 5 to 20 g/10 min; and a metallocene-produced LDPE polymer, the LDPE polymer being a copolymer of ethylene and at least one C3 to C12 alpha olefin and having a density of from 0.916 to 0.940 g/cm3 and a melt index of from 0.5 to 15 g/10 min. In this embodiment, the blend includes 5-95% by weight of the VLDPE polymer and 95-5% by weight of the LDPE polymer, based on the total weight of the VLDPE and LDPE polymers.
In another embodiment, the present invention is directed to a polymer blend, the blend including a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and 1-butene, 1-hexene or 1-octene and having a density of from 0.910 to 0.915 g/cm3, a melt index of from 5 to 20 g/10 min, a composition distribution breadth index (CDBI) of 60 to 80 wt % and a molecular weight distribution (MWD) of 2.2 to 2.8; and a metallocene-produced LDPE polymer, the LDPE polymer being a copolymer of ethylene and 1-butene, 1-hexene or 1-octene and having a density of from 0.916 to 0.925 g/Cm3 and a melt index of from 0.5 to 10 g/10 min. In this embodiment, the blend preferably includes 10-90% by weight of the VLDPE polymer and 90-10% by weight of the LDPE polymer, based on the total weight of the VLDPE and LDPE polymers.
In one embodiment, the present invention is directed to a VLDPE/LDPE polymer blend, the blend including a metallocene-produced VLDPE polymer comprising an ethylene copolymer with a comonomer content of 25% or less by weight, preferably 20% or less by weight, and more preferably 15% or less by weight.
In another embodiment, the present invention is directed to a polymer blend, the blend including from 1 to 99% by weight of a copolymer derived from ethylene and one or more C3-C20 alpha olefin comonomers, and from 1 to 99% by weight of a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm3, wherein the sum of the weight of the copolymer and low density polyethylene polymer is 100%. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, a density of less than 0.916 g/cm3, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, and a molecular weight distribution Mz/Mw of less than 2.
In another embodiment, the present invention is directed to an article, the article including a substrate and a film disposed on the substrate. The film includes a polymer blend, the polymer blend including from 1 to 99% by weight of a copolymer derived from ethylene and one or more C3-C20 alpha olefin comonomers, and from 1 to 99% by weight of a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm3, wherein the sum of the weight of the copolymer and the low density polyethylene polymer is 100%. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, a density of less than 0.916 g/cm3, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, and a molecular weight distribution Mz/Mw of less than 2.
In another embodiment, the present invention is directed to a polymer blend composition, the composition including (a) a copolymer derived from ethylene and one or more C3-C20 alpha olefin comonomers and (b) a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm3. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, a density of less than 0.916 g/cm3, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, a molecular weight distribution Mw/Mw of less than 2, and a bi-modal composition distribution.
In another embodiment, the present invention is directed to a monolayer film formed from a blend including (a) a copolymer derived from ethylene and one or more C3-C20 alpha olefin comonomers and (b) a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm3. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, a density of less than 0.916 g/cm3, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, a molecular weight distribution Mz/Mw of less than 2, and a bi-modal composition distribution.
In another embodiment, the present invention is directed to a multilayer film, the film including a first layer and a second layer, and at least one of the layers including a polymer blend composition. The polymer blend composition includes (a) a copolymer derived from ethylene and one or more C3-C20 alpha olefin comonomers and (b) an LDPE polymer having a density of from 0.916 to 0.928 g/cm3. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, A density of less than 0.916 g/cm3, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, a molecular weight distribution Mz/Mw of less than 2, and a bi-modal composition distribution.
In another embodiment, the present invention is directed to a polymer blend composition, the composition including a metallocene-catalyzed linear very low density polyethylene polymer and a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm3. The very low density polyethylene polymer is further characterized by properties including one or more of the following: a density of less than 0.916 g/cm3, a composition distribution breadth index of 50 to 85% by weight, a molecular weight distribution Mw/Mn of 2 to 3, and a molecular weight distribution Mz/Mw of less than 2.
Polyethylene has Two Peaks in a TREF Measurement
In another embodiment, the present invention provides a polymeric film, the film being extrusion cast from a blend of a metallocene-produced VLDPE polymer and an LDPE, as described above.
In another embodiment, the present invention is directed to monolayer films formed from the polymer blends of the invention.
In another embodiment, the present invention is directed to multilayer films, wherein at least one layer of the multilayer film is formed of a polymer blend of the invention.
In other embodiments, the invention is directed to articles including the films of the invention, articles wrapped with the films of the invention, and substrates coated with the films of the invention.
In another embodiment, the present invention provides an article of manufacture, the article including a flexible substrate and a polymeric film extrusion-coated on the substrate, wherein the polymeric film is a blend of a metallocene-produced VLDPE polymer and an LDPE as described above. The substrate can be a flexible material, such as paper, a metal foil, a flexible polymeric material, or other flexible substrate capable of being coated.
The blends and films of the present invention show improved mechanical and/or sealing properties, relative to prior art LDPE and LLDPE materials.
4.1 VLDPE Polymers
The polymer blends and films of the present invention include a very low density polyethylene (VLDPE) polymer. As used herein, the terms xe2x80x9cvery low density polyethylenexe2x80x9d polymer and xe2x80x9cVLDPExe2x80x9d polymer refer to a polyethylene homopolymer or preferably copolymer having a density of less than 0.916 g/cm3. Polymers having more than two types of monomers, such as terpolymers, are also included within the term xe2x80x9ccopolymerxe2x80x9d as used herein. The comonomers that are useful in general for making VLDPE copolymers include xcex1-olefins, such as C3-C20 xcex1-olefins and preferably C3-C12 xcex1-olefins. The xcex1-olefin comonomer can be linear or branched, and two or more comonomers can be used, if desired. Examples of suitable comonomers include linear C3-C12 xcex1-olefins, and xcex1-olefins having one or more C1-C3 alkyl branches, or an aryl group. Specific examples include propylene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl or propyl substituents; 1-hexene with one or more methyl, ethyl or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-octene with one or more methyl, ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl or propyl substituents; ethyl, methyl or dimethyl-substituted 1-decene; 1-dodecene; and styrene. It should be appreciated that the list of comonomers above is merely exemplary, and is not intended to be limiting. Preferred comonomers include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and styrene.
Other useful comonomers include conjugated and non-conjugated dienes, acetylene, which can be included in minor amounts in terpolymer compositions. Non-conjugated dienes useful as co-monomers preferably are straight chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms. Suitable non-conjugated dienes include, for example: (a) straight chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as 1,4-cyclohexadiene; 1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene; norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of the non-conjugated dienes typically used, the preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and tetracyclo-(xcex94-11,12)-5,8-dodecene. Particularly preferred diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB). Note that throughout this description the terms xe2x80x9cnon-conjugated dienexe2x80x9d and xe2x80x9cdienexe2x80x9d are used interchangeably.
It should be appreciated that the amount of comonomer used will depend upon the desired density of the VLDPE polymer and the specific comonomers selected. In general, the comonomer will be present in an amount of from 0 to 15% by weight, typically 5 to 15% by weight for preferred comonomers such as butene, hexene and octene. It is well-understood in the art that, for a given comonomer, the density of the VLDPE polymer produced therefrom decreases as the comonomer content increases. One skilled in the art can readily determine the appropriate comonomer content appropriate to produce a VLDPE polymer having a desired density.
The VLDPE polymer has a density of less than 0.916 g/cm3, and preferably at least 0.890 g/cm3, more preferably at least 0.900 g/cm3. Thus, a preferred density range for the VLDPE polymer is 0.900 g/cm3 to 0.915 g/cm3. Alternate lower limits of the VLDPE polymer density include 0.905 g/cm3 or 0.910 g/cm3.
The VLDPE polymer is further characterized by a melt index (MI) of from 0.5 to 20 g/10 min (dg/min), as measured in accordance with ASTM-1238 condition E. In one or more specific embodiments, alternative lower limits for the melt index include 0.7 and 1.0 g/10 min, and alternative upper limits for the melt index include 5, 10 and 15 g/10 min, with melt index ranges from any lower limit to any upper limit being within the scope of the invention.
In one embodiment, the VLDPE polymer is made in a metallocene-catalyzed polymerization process. As used herein, the terms xe2x80x9cmetallocene-catalyzed VLDPE,xe2x80x9d xe2x80x9cmetallocene-produced VLDPE,xe2x80x9d or xe2x80x9cm-VLDPExe2x80x9d refer to a VLDPE polymer having the density and melt index properties described herein, and being produced in the presence of a metallocene catalyst. One skilled in the art will recognize that a metallocene-catalyzed VLDPE polymer has measurable properties distinguishable from a VLDPE polymer having the same comonomers in the same weight percentages but produced from a different process, such as a conventional Ziegler-Natta polymerization process.
The terms xe2x80x9cmetallocenexe2x80x9d and xe2x80x9cmetallocene catalyst precursorxe2x80x9d as used herein mean compounds having a Group 4, 5 or 6 transition metal (M), with a cyclopentadienyl (Cp) ligand or ligands which may be substituted, at least one non-cyclopentadienyl-derived ligand (X), and zero or one heteroatom-containing ligand (Y), the ligands being coordinated to M and corresponding in number to the valence thereof. The metallocene catalyst precursors generally require activation with a suitable co-catalyst (referred to as an xe2x80x9cactivatorxe2x80x9d), in order to yield an xe2x80x9cactive metallocene catalystxe2x80x9d, i.e., an organometallic complex with a vacant coordination site that can coordinate, insert, and polymerize olefins. The metallocene catalyst precursor is preferably one of, or a mixture of metallocene compounds of either or both of the following types:
(1) Cyclopentadienyl (Cp) complexes which have two Cp ring systems for ligands. The Cp ligands form a sandwich complex with the metal and an be free to rotate (unbridged) or locked into a rigid configuration through a bridging group. The Cp ring ligands can be like or unlike, unsubstituted, substituted, or a derivative thereof, such as a heterocyclic ring system which may be substituted, and the substitutions can be fused to form other saturated or unsaturated rings systems such as tetrahydroindenyl, indenyl, or fluorenyl ring systems. These cyclopentadienyl complexes have the general formula
(Cp1R1m)R3n(Cp2R2p)MXq
wherein: Cp1 and Cp2 are the same or different cyclopentadienyl rings; R1 and R2 are each, independently, a halogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms; m is 0 to 5; p is 0 to 5; two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring containing from 4 to about 20 carbon atoms; R3 is a bridging group; n is the number of atoms in the direct chain between the two ligands and is 0 to 8, preferably 0 to 3; M is a transition metal having a valence of from 3 to 6, preferably from group 4, 5, or 6 of the periodic table of the elements and is preferably in its highest oxidation state; each X is a non-cyclopentadienyl ligand and is, independently, a halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms; and q is equal to the valence of M minus 2.
(2) Monocyclopentadienyl complexes which have only one Cp ring system as a ligand. The Cp ligand forms a half-sandwich complex with the metal and can be free to rotate (unbridged) or locked into a rigid configuration through a bridging group to a heteroatom-containing ligand. Bridged structures can be meso-configurations or racemic stereoisomers, or a mixture thereof. The Cp ring ligand can be unsubstituted, substituted, or a derivative thereof such as a heterocyclic ring system which may be substituted, and the substitutions can be fused to form other saturated or unsaturated rings systems such as tetrahydroindenyl, indenyl, or fluorenyl ring systems. The heteroatom containing ligand is bound to both the metal and optionally to the Cp ligand through the bridging group. The heteroatom itself is an atom with a coordination number of three from group 15 or 16 of the periodic table of the elements. These mono-cyclopentadienyl complexes have the general formula
(Cp1R1m)R3n(YrR2)MXs
wherein: each R1 is independently, a halogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, xe2x80x9cmxe2x80x9d is 0 to 5, and two R1 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated there with can be joined together to form a ring containing from 4 to about 20 carbon atoms; R3 is a bridging group; xe2x80x9cnxe2x80x9d is 0 to 3; M is a transition metal having a valence of from 3 to 6, preferably from group 4, 5, or 6 of the periodic table of the elements and is preferably in its highest oxidation state; Y is a heteroatom containing group in which the heteroatom is an element with a coordination number of three from Group VA or a coordination number of two from group VIA, preferably nitrogen, phosphorous, oxygen, or sulfur; R2 is a radical selected from a group consisting of C1 to C20 hydrocarbon radicals, substituted C1 to C20 hydrocarbon radicals, wherein one or more hydrogen atoms is replaced with a halogen atom, and when Y is three coordinate and unbridged there may be two R2 groups on Y each independently a radical selected from the group consisting of C1 to C20 hydrocarbon radicals, substituted C1 to C20 hydrocarbon radicals, wherein one or more hydrogen atoms is replaced with a halogen atom, and each X is a non-cyclopentadienyl ligand and is, independently, a halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, xe2x80x9csxe2x80x9d is equal to the valence of M minus 2.
Examples of biscyclopentadienyl metallocenes of the type described in group (1) above for producing the m-VLDPE polymers of the invention are disclosed in U.S. Pat. Nos. 5,324,800; 5,198,401; 5,278,119; 5,387,568; 5,120,867; 5,017,714; 4,871,705; 4,542,199; 4,752,597; 5,132,262; 5,391,629; 5,243,001; 5,278,264; 5,296,434; and 5,304,614.
Illustrative, but not limiting, examples of suitable bridged biscyclopentadienyl metallocenes of the type described in group (1) above are the racemic isomers of:
xcexc-(CH3)2Si(indenyl)2M(Cl)2;
xcexc-(CH3)2Si(indenyl)2M(CH3)2;
xcexc-(CH3)2Si(tetrahydroindenyl)2M(Cl)2;
xcexc-(CH3)2Si(tetrahydroindenyl)2M(CH3)2;
xcexc-(CH3)2Si(indenyl)2M(CH2CH3)2; and
xcexc-(C6H5)2C(indenyl)2M(CH3)2;
wherein M is Zr or Hf.
Examples of suitable unsymmetrical cyclopentadienyl metallocenes of the type described in group (1) above are disclosed in U.S. Pat. Nos. 4,892,851; 5,334,677; 5,416,228; and 5,449,651; and in the publication J. Am. Chem. Soc. 1988, 110, 6255.
Illustrative, but not limiting, examples of preferred unsymmetrical cyclopentadienyl metallocenes of the type described in group (1) above are:
xcexc-(C6H5)2C(cyclopentadienyl)(fluorenyl)M(R)2;
xcexc-(C6H5)2C(3-methylcyclopentadienyl)(fluorenyl)M(R)2;
xcexc-(CH3)2C(cyclopentadienyl)(fluorenyl)M(R)2;
xcexc-(C6H5)2C(cyclopentadienyl)(2-methylindenyl)M(CH3)2;
xcexc-(C6H5)2C(3-methylcyclopentadienyl)(2-methylindenyl)M(Cl)2;
xcexc-(C6H5)2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)2; and
xcexc-(CH3)2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)2;
wherein M is Zr or Hf, and R is Cl or CH3.
Examples of suitable monocyclopentadienyl metallocenes of the type described in group (2) above are disclosed in U.S. Pat. Nos. 5,026,798; 5,057,475; 5,350,723; 5,264,405; 5,055,438; and in WO 96/002244.
Illustrative, but not limiting, examples of preferred monocyclopentadienyl metallocenes of the type described in group (2) above are:
xcexc-(CH3)2Si(cyclopentadienyl)(1-adamantylamido)M(R)2;
xcexc-(CH3)2Si(3-tertbutylcyclopentadienyl)(1-adamantylamido)M(R)2;
xcexc-(CH2(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2;
xcexc-(CH3)2Si(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2;
xcexc-(CH3)2C(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2;
xcexc-(CH3)2Si(tetramethylcyclopentadienyl)(1-tertbutylamido)M(R)2;
xcexc-(CH3)2Si(fluorenyl)(1-tertbutylamido)M(R)2;
xcexc-(CH3)2Si(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)2;
and
xcexc-(C6H5)2C(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)2;
wherein M is Ti, Zr or Hf, and R is Cl or CH3.
Another class of organometallic complexes that are useful catalysts for the VLDPE polymers described herein are those with diimido ligand systems, such as are described in WO 96/23010.
The metallocene compounds are contacted with an activator to produce an active catalyst. One class of activators is noncoordinating anions, where the term xe2x80x9cnoncoordinating anionxe2x80x9d (NCA) means an anion which either does not coordinate to the transition metal cation or which is only weakly coordinated to the transition metal cation, thereby remaining sufficiently labile to be displaced by a neutral Lewis base. xe2x80x9cCompatiblexe2x80x9d noncoordinating anions are those which are not degraded to neutrality when the initially formed complex decomposes. Further, the anion will not transfer an anionic substituent or fragment to the cation so as to cause it to form a neutral four coordinate metallocene compound and a neutral by-product from the anion. Noncoordinating anions useful in accordance with this invention are those which are compatible, stabilize the metallocene cation in the sense of balancing its ionic charge in a +1 state, yet retain sufficient lability to permit displacement by an ethylenically or acetylenically unsaturated monomer during polymerization. Additionally, the anions useful in this invention will be large or bulky in the sense of sufficient molecular size to largely inhibit or prevent neutralization of the metallocene cation by Lewis bases other than the polymerizable monomers that may be present in the polymerization process. Typically the anion will have a molecular size of greater than or equal to about 4 angstroms.
An additional method of making metallocene catalysts uses ionizing anionic pre-cursors which are initially neutral Lewis acids but form the cation and anion upon ionizing reaction with the metallocene compounds. For example, tris(pentafluorophenyl) boron acts to abstract an alkyl, hydride or silyl ligand from the metallocene compound to yield a metallocene cation and a stabilizing non-coordinating anion; see, EP-A-0 427 697 and EP-A-0 520 732. Metallocene catalysts for addition polymerization can also be prepared by oxidation of the metal centers of transition metal compounds by anionic precursors containing metallic oxidizing groups along with the anion groups; see EP-A-0 495 375.
Examples of suitable activators capable of ionic cationization of the metallocene compounds of the invention, and consequent stabilization with a resulting noncoordinating anion, include:
trialkyl-substituted ammonium salts such as:
triethylammonium tetraphenylborate;
tripropylammonium tetraphenylborate;
tri(n-butyl)ammonium tetraphenylborate;
trimethylammonium tetrakis(p-tolyl)borate;
trimethylammonium tetrakis(o-tolyl)borate;
tributylammonium tetrakis(pentafluorophenyl)borate;
tripropylammonium tetrakis(o,p-dimethylphenyl)borate;
tributylammonium tetrakis(m,m-dimethylphenyl)borate;
tributylammonium tetrakis(p-trifluoromethylphenyl)borate;
tributylammonium tetrakis(pentafluorophenyl)borate; and
tri(n-butyl)ammonium tetrakis(o-tolyl)borate;
N,N-dialkyl anilinium salts such as:
N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate;
N,N-dimethylaniliniumtetrakis(heptafluoronaphthyl)borate;
N,N-dimethylanilinium tetrakis(perfluoro-4-biphenyl)borate;
N,N-dimethylanilinium tetraphenylborate;
N,N-diethylanilinium tetraphenylborate; and
N,N-2,4,6-pentamethylanilinium tetraphenylborate;
dialkyl ammonium salts such as:
di-(isopropyl)ammonium tetrakis(pentafluorophenyl)borate; and
dicyclohexylammonium tetraphenylborate; and
triaryl phosphonium salts such as:
triphenylphosphonium tetraphenylborate;
tri(methylphenyl)phosphonium tetraphenylborate; and
tri(dimethylphenyl)phosphonium tetraphenylborate.
Further examples of suitable anionic precursors include those including a
stable carbonium ion, and a compatible non-coordinating anion. These include:
tropillium tetrakis(pentafluorophenyl)borate;
triphenylmethylium tetrakis(pentafluorophenyl)borate;
benzene (diazonium) tetrakis(pentafluorophenyl)borate;
tropillium phenyltris(pentafluorophenyl)borate;
triphenylmethylium phenyl-(trispentafluorophenyl)borate;
benzene (diazonium) phenyl-tris(pentafluorophenyl)borate;
tropillium tetrakis(2,3,5,6-tetrafluorophenyl)borate;
triphenylmethylium tetrakis(2,3,5,6-tetrafluorophenyl)borate;
benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)borate;
tropillium tetrakis(3,4,5-trifluorophenyl)borate;
benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)borate;
tropillium tetrakis(3,4,5-trifluorophenyl)aluminate;
triphenylmethylium tetrakis(3,4,5-trifluorophenyl)aluminate;
benzene (diazonium) tetrakis(3,4,5-trifluorophenyl)aluminate;
tropillium tetrakis(1,2,2-trifluoroethenyl)borate;
triphenylmethylium tetrakis(1,2,2-trifluoroethenyl)borate;
benzene (diazonium) tetrakis(1,2,2-trifluoroethenyl)borate;
tropillium tetrakis(2,3,4,5-tetrafluorophenyl)borate;
triphenylmethylium tetrakis(2,3,4,5-tetrafluorophenyl)borate; and
benzene (diazonium) tetrakis(2,3,4,5-tetrafluorophenyl)borate.
Where the metal ligands include halide moieties, for example, (methyl-phenyl) silylene(tetra-methyl-cyclopentadienyl)(tert-butyl-amido) zirconium dichloride), which are not capable of ionizing abstraction under standard conditions, they can be converted via known alkylation reactions with organometallic compounds such as lithium or aluminum hydrides or alkyls, alkylalumoxanes, Grignard reagents, etc. See EP-A-0 500 944, EP-A1-0 570 982 and EP-A1-0 612 768 for processes describing the reaction of alkyl aluminum compounds with dihalide substituted metallocene compounds prior to or with the addition of activating anionic compounds. For example, an aluminum alkyl compound may be mixed with the metallocene prior to its introduction into the reaction vessel. Since the alkyl aluminum is also suitable as a scavenger (as described below), its use in excess of that normally stoichiometrically required for akylation of the metallocene will permit its addition to the reaction solvent with the metallocene compound. Normally, alumoxane would not be added with the metallocene, so as to avoid premature activation, but can be added directly to the reaction vessel in the presence of the polymerizable monomers when serving as both scavenger and alkylating activator.
Alkylalumoxanes are additionally suitable as catalyst activators, particularly for those metallocenes having halide ligands. An alumoxane useful as a catalyst activator typically is an oligomeric aluminum compound represented by the general formula (Rxe2x80x94Alxe2x80x94O)n, which is a cyclic compound, or R(Rxe2x80x94Alxe2x80x94O)nAlR2, which is a linear compound. In these formulae, each R or R2 is a C1 to C5 alkyl radical, for example, methyl, ethyl, propyl, butyl or pentyl, and xe2x80x9cnxe2x80x9d is an integer from 1 to about 50. Most preferably, R is methyl and xe2x80x9cnxe2x80x9d is at least 4, i.e., methylalumoxane (MAO). Alumoxanes can be prepared by various procedures known in the art. For example, an aluminum alkyl may be treated with water dissolved in an inert organic solvent, or it may be contacted with a hydrated salt, such as hydrated copper sulfate suspended in an inert organic solvent, to yield an alumoxane. Generally, however prepared, the reaction of an aluminum alkyl with a limited amount of water yields a mixture of the linear and cyclic species of the alumoxane.
Preferably, a scavenging compound is also used. The term xe2x80x9cscavenging compoundxe2x80x9d as used herein refers to those compounds effective for removing polar impurities from the reaction solvent. Such impurities can be inadvertently introduced with any of the polymerization reaction components, particularly with solvent, monomer and comonomer feed, and adversely affect catalyst activity and stability by decreasing or even eliminating catalytic activity, particularly when a metallocene cation-noncoordinating anion pair is the catalyst system. The polar impurities, or catalyst poisons, include water, oxygen, oxygenated hydrocarbons, metal impurities, etc. Preferably, steps are taken before provision of such into the reaction vessel, for example, by chemical treatment or careful separation techniques after or during the synthesis or preparation of the various components, but some minor amounts of scavenging compound will still normally be required in the polymerization process itself. Typically, the scavenging compound will be an organometallic compound such as the Group-13 organometallic compounds of U.S. Pat. Nos. 5,153,157 and 5,241,025; EP-A-0 426 638; WO-A-91/09882; WO-A-94/03506; and WO-A-93/14132. Exemplary compounds include triethyl aluminum, triethyl borane, tri-isobutyl aluminum, isobutyl aluminumoxane, those having bulky substituents covalently bound to the metal or metalloid center being preferred to minimize adverse interaction with the active catalyst.
The catalyst system is preferably supported on a carrier, typically an inorganic oxide or chloride or a resinous material such as polyethylene. Preferably, the catalyst system includes a metallocene component with single or multiple cyclopentadienyl components reacted with either a metal alkyl or alkoxy component or an ionic compound component. These catalysts can include partially and/or fully activated precursor compositions. The catalysts may be modified by prepolymerization or encapsulation. Specific metallocenes and catalyst systems useful in practicing the invention are disclosed in WO 96/11961, and WO 96/11960. Other non-limiting examples of metallocene catalysts and catalyst systems are discussed in U.S. Pat. Nos. 4,808,561, 5,017,714, 5,055,438, 5,064,802, 5,124,418, 5,153,157 and 5,324,800.
The invention VLDPEs can be made using a gas phase polymerization process. As used herein, the term xe2x80x9cgas phase polymerizationxe2x80x9d refers to polymerization of polymers from monomers in a gas fluidized bed. Generally, the VLDPEs of the present invention may be made by polymerizing alpha-olefins in the presence of a metallocene catalyst under reactive conditions in a gas phase reactor having a fluidized bed and a fluidizing medium. In a specific embodiment, the VLDPE polymer can be made by polymerization in a single reactor (as opposed to multiple reactors). As discussed in greater detail below, a variety of gas phase polymerization processes may be used. For example, polymerization may be conducted in uncondensed or xe2x80x9cdryxe2x80x9d mode, condensed mode, or xe2x80x9csuper-condensed mode.xe2x80x9d In a specific embodiment, the liquid in the fluidizing medium can be maintained at a level greater than 2 weight percent based on the total weight of the fluidizing medium.
The material exiting the reactor includes a very low density polyethylene (VLDPE), having a density from 0.890 to 0.915 g/cm3, more preferably a density from 0.910 to 0.915 g/cm3, and a stream containing unreacted monomer gases. Following polymerization, the polymer is recovered. In certain embodiments, the stream can be compressed and cooled, and mixed with feed components, whereupon a gas phase and a liquid phase are then returned to the reactor.
In a preferred aspect, the invention VLDPEs are copolymers, made from ethylene monomers together with at least one comonomer, e.g., hexene or octene. Polymers having more than two types of monomers, such as terpolymers, are also included within the term xe2x80x9ccopolymerxe2x80x9d as used herein. For example, VLDPE terpolymers may be made, using ethylene monomer together with any two of butene, hexene and octene. For one embodiment of the VLDPE polymer comprising an ethylene/butene copolymer, the molar ratio of butene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030. For one embodiment of the VLDPE polymer comprising an ethylene/hexene copolymer, the molar ratio of hexene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030. For one embodiment of the VLDPE polymer comprising an ethylene/octene copolymer, the molar ratio of octene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030.
The comonomers that are useful in general for making VLDPE copolymers include xcex1-olefins, such as C3-C20 xcex1-olefins and preferably C3-C12 xcex1-olefins. The xcex1-olefin comonomer can be linear or branched, and two or more comonomers can be used, if desired. Examples of suitable comonomers include linear C3-C12 xcex1-olefins, and xcex1-olefins having one or more C1-C3 alkyl branches, or an aryl group. Specific examples include propylene; 1-butene, 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl or propyl substituents; 1-hexene with one or more methyl, ethyl or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-octene with one or more methyl, ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl or propyl substituents; ethyl, methyl or dimethyl-substituted 1-decene; 1-dodecene; and styrene. It should be appreciated that the list of comonomers above is merely exemplary, and is not intended to be limiting. Preferred comonomers include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and styrene, more preferably 1-butene, 1-hexene, and 1-octene.
Although not generally preferred, other useful comonomers include polar vinyl, conjugated and non-conjugated dienes, acetylene and aldehyde monomers, which can be included in minor amounts in terpolymer compositions. Non-conjugated dienes useful as co-monomers preferably are straight chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms. Suitable non-conjugated dienes include, for example: (a) straight chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as 1,4-cyclohexadiene; 1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene; norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of the non-conjugated dienes typically used, the preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and tetracyclo-(xcex94-11,12)-5,8-dodecene. Particularly preferred diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB). Note that throughout this description the terms xe2x80x9cnon-conjugated dienexe2x80x9d and xe2x80x9cdienexe2x80x9d are used interchangeably.
It should be appreciated that the amount of comonomer used will depend upon the desired density of the VLDPE polymer and the specific comonomers selected. In general, the comonomer may be present in an amount of 25% or less by weight, preferably 20% or less by weight and more preferably 15% or less by weight. In one embodiment, the comonomer may be present in an amount of 5% or more by weight. For a given comonomer, the density of the VLDPE polymer produced therefrom decreases as the comonomer content increases. One skilled in the art can readily determine the appropriate comonomer content appropriate to produce a VLDPE polymer having a desired density.
Generally, in carrying out the gas phase polymerization processes described herein, the reactor temperature can be in the range of 50xc2x0 C. to 110xc2x0 C., sometimes higher. However, the reactor temperature should not exceed the melting point of the VLDPE being formed. A typical reactor temperature is 80xc2x0 C. The reactor pressure should be 100 to 1000 psig (689 kPa to 6,895 kPa), preferably 150 to 600 psig (1034 to 4137 kPa), more preferably 200 to 500 psig (1379 to 3448 kPa) and most preferably 250 to 400 psig (1723 to 2758 kPa).
Preferably, the process is operated in a continuous cycle. A specific, non-limiting embodiment of the gas phase polymerization process that is operated in a continuous cycle will now be described, it being understood that other forms of gas polymerization may also be used.
A gaseous stream containing one or more monomers is continuously passed through a fluidized bed under reactive conditions in the presence of a metallocene catalyst. This gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product may be withdrawn from the reactor and new monomer or monomers are added to replace the reacted monomer(s). In one part of the cycle, in a reactor, a cycling gas stream is heated by the heat of polymerization. This heat is removed in another part of the cycle by a cooling system external to the reactor. Heat generated by the reaction may be removed in order to maintain the temperature of the gaseous stream inside the reactor at a temperature below the polymer and catalyst degradation temperatures. Further, it is often desirable to prevent agglomeration or formation of chunks of polymer that cannot be removed as product. This may be accomplished in a variety of ways known in the art, such as, for example, through control of the temperature of the gaseous stream in the reaction bed to a temperature below the fusion or sticking temperature of the polymer particles produced during the polymerization reaction.
Heat should be removed, since the amount of polymer produced in the fluidized bed polymerization process is generally related to the amount of heat that can be withdrawn from a reaction zone in a fluidized bed within the reactor. During the gas phase polymerization process, heat can be removed from the gaseous recycle stream by cooling the stream outside the reactor. The velocity of the gaseous recycle stream in a fluidized bed process should be sufficient to maintain the fluidized bed in a fluidized state. In certain conventional fluidized bed reactors, the amount of fluid circulated to remove the heat of polymerization is often greater than the amount of fluid required for support of the fluidized bed and for adequate mixing of the solids in the fluidized bed. However, to prevent excessive entrainment of solids in a gaseous stream withdrawn from the fluidized bed, the velocity of the gaseous stream should be regulated.
The recycle stream can be cooled to a temperature below the dew point, resulting in condensing a portion of the recycle stream, as described in U.S. Pat. Nos. 4,543,399 and 4,588,790. As set forth in those patents, the resulting stream containing entrained liquid should be returned to the reactor without the aforementioned agglomeration and/or plugging that may occur when a liquid is introduced during the fluidized bed polymerization process. For purposes of this patent, this intentional introduction of a liquid into a recycle stream or reactor during the process is referred to generally as a xe2x80x9ccondensed modexe2x80x9d operation of the gas phase polymerization process. As taught by the above mentioned patents, when a recycle stream temperature is lowered to a point below its dew point in condensed mode operation, an increase in polymer production is possible, as compared to production in a xe2x80x9cnon-condensingxe2x80x9d or xe2x80x9cdryxe2x80x9d mode, because of increased cooling capacity. Also, a substantial increase in space time yield, the amount of polymer production in a given reactor volume, can be achieved by operating in condensed mode with little or no change in product properties. Also, in certain condensed mode operations, the liquid phase of the two-phase gas/liquid recycle stream mixture remains entrained or suspended in the gas phase of the mixture. The cooling of the recycle stream to produce this two-phase mixture results in a liquid/vapor equilibrium. Vaporization of the liquid occurs when heat is added or pressure is reduced. The increase in space time yields are the result of this increased cooling capacity of the recycle stream which, in turn, is due both to the greater temperature differential between the entering recycle stream and the fluidized bed temperature and to the vaporization of condensed liquid entrained in the recycle stream. In a specific non-limiting embodiment of the process described herein, a condensed mode of operation is utilized.
In operating the gas phase polymerization process to obtain the VLDPEs of this invention, the amount of polymer and catalyst, the operating temperature of the reactor, the ratio of comonomer(s) to monomer and the ratio of hydrogen to monomer should be determined in advance, so that the desired density and melt index can be achieved.
Although a variety of gas polymerization processes may be used to make the polyolefins of the present inventions, including non-condensed or dry mode, it is preferred to use any one of a variety of condensed mode processes, including the condensed mode processes described in the above patents, as well as improved condensed mode gas polymerization processes, such as those disclosed in U.S. Pat. Nos. 5,462,999, and 5,405,922. Other types of condensed mode processes are also applicable, including so-called xe2x80x9csupercondensed modexe2x80x9d processes, as discussed in U.S. Pat. Nos. 5,352,749 and 5,436,304.
The condensable fluids that can be used in one of the condensed mode gas phase polymerization operations may include saturated or unsaturated hydrocarbons. Examples of suitable inert condensable fluids are readily volatile liquid hydrocarbons, which may be selected from saturated hydrocarbons containing from 2 to 8 carbon atoms. Some suitable saturated hydrocarbons are propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, isohexane, and other saturated C6 hydrocarbons, n-heptane, n-octane and other saturated C7 and C8 hydrocarbons, or mixtures thereof. The preferred inert condensable hydrocarbons are C4 and C6 saturated hydrocarbons. The condensable fluids may also include polymerizable condensable comonomers such as olefins, alpha-olefins, diolefins, diolefins containing at least one alpha-olefin or mixtures thereof including some of the aforementioned monomers which may be partially or entirely incorporated into the polymer product.
The density of the polyethylene having the improved properties of this invention ranges from 0.890 to 0.915 g/cm3, preferably from 0.910 to 0.915 g/cm3, more preferably from 0.911 to 0.913 g/cm3. Preferably, the polymers have a melt index (MI) ranging from 0.01 to 20.0, preferably 0.5 to 15.0. Melt index is measured according to ASTM-1238 condition E.
The preferred gas-phase, metallocene VLDPE polymers can be further characterized by a narrow composition distribution. As is well known to those skilled in the art, the composition distribution of a copolymer relates to the uniformity of distribution of comonomer among the molecules of the polymer. Metallocene catalysts are known to incorporate comonomer very evenly among the polymer molecules they produce. Thus, copolymers produced from a catalyst system having a single metallocene component have a very narrow composition distribution, in that most of the polymer molecules will have roughly the same comonomer content, and within each molecule the comonomer will be randomly distributed. By contrast, conventional Ziegler-Natta catalysts generally yield copolymers having a considerably broader composition distribution, with comonomer inclusion varying widely among the polymer molecules.
A measure of composition distribution is the xe2x80x9cComposition Distribution Breadth Indexxe2x80x9d (xe2x80x9cCDBIxe2x80x9d). The definition of Composition Distribution Breadth Index (CDBI), and the method of determining CDBI, can be found in U.S. Pat. No. 5,206,075 and PCT publication WO 93/03093. From the weight fraction versus composition distribution curve, the CDBI is determined by establishing the weight percentage of a sample that has a comonomer content within 50% of the median comonomer content on each side of the median. The CDBI of a copolymer is readily determined utilizing well known techniques for isolating individual fractions of a sample of the copolymer. One such technique is Temperature Rising Elution Fractionation (TREF) as described in Wild, et al., J. Poly. Sci., Poly. Phys. Ed., vol. 20, p. 441 (1982).
To determine CDBI, a solubility distribution curve is first generated for the copolymer. This may be accomplished using data acquired from the TREF technique described above. This solubility distribution curve is a plot of the weight fraction of the copolymer that is solubilized as a function of temperature. This is converted to a weight fraction versus composition distribution curve. For the purpose of simplifying the correlation of composition with elution temperature, all fractions are assumed to have a Mnxe2x89xa715,000, where Mn is the number average molecular weight of the fraction. Any low weight fractions present generally represent a trivial portion of the VLDPE polymers. The remainder of this description and the appended claims maintain this convention of assuming all fractions have Mnxe2x89xa715,000 in the CDBI measurement.
The VLDPE polymers can also be characterized by molecular weight distribution (MWD). Molecular weight distribution (MWD) is a measure of the range of molecular weights within a given polymer sample. It is well known that the breadth of the MWD can be characterized by the ratios of various molecular weight averages, such as the ratio of the weight average molecular weight to the number average molecular weight, Mw/Mn, or the ratio of the Z-average molecular weight to the weight average molecular weight, Mz/Mw.
Mz, Mw and Mn can be measured using gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC). This technique utilizes an instrument containing columns packed with porous beads, an elution solvent, and detector in order to separate polymer molecules of different sizes. In a typical measurement, the GPC instrument used is a Waters chromatograph equipped with ultrastyro gel columns operated at 145xc2x0 C. The elution solvent used is trichlorobenzene. The columns are calibrated using sixteen polystyrene standards of precisely known molecular weights. A correlation of polystyrene retention volume obtained from the standards, to the retention volume of the polymer tested yields the polymer molecular weight.
Average molecular weights M can be computed from the expression:   M  =                    ∑        i            ⁢                        N          i                ⁢                  M          i                      n            +            1                                              ∑        i            ⁢                        N          i                ⁢                  M          i          n                    
where Ni is the number of molecules having a molecular weight Mi. When n=0, M is the number average molecular weight Mn. When n=1, M is the weight average molecular weight Mw. When n=2, M is the Z-average molecular weight Mz. The desired MWD function (e.g., Mw/Mn or Mz/Mw) is the ratio of the corresponding M values. Measurement of M and MWD is well known in the art and is discussed in more detail in, for example, Slade, P. E. Ed., Polymer Molecular Weights Part II, Marcel Dekker, Inc., NY, (1975) 287-368; Rodriguez, F., Principles of Polymer Systems 3rd ed., Hemisphere Pub. Corp., N.Y., (1989) 155-160; U.S. Pat. No. 4,540,753; Verstrate et al., Macromolecules, vol. 21, (1988) 3360; and references cited therein.
The VLDPE polymers recited in the claims below are preferably linear polymers, i.e., without long chain branching. As used in the present disclosure, the term xe2x80x9clinearxe2x80x9d is applied to a polymer that has a linear backbone and does not have long chain branching; i.e., a xe2x80x9clinearxe2x80x9d polymer is one that does not have the long chain branches characteristic of a SLEP polymer as defined in U.S. Pat. Nos. 5,272,236 and 5,278,272. Thus, a xe2x80x9csubstantially linearxe2x80x9d polymer as disclosed in those patents is not a xe2x80x9clinearxe2x80x9d polymer because of the presence of long chain branching.
Preferred VLDPE polymers have one or more of the following characteristics, in addition to the density, melt index, and other parameters described herein:
(a) a composition distribution CDBI of 50 to 85%, alternatively 60 to 80%, or 55 to 75%, or 55% or more to 70% or less;
(b) a molecular weight distribution MWD of 2 to 3, alternatively 2.2 to 2.8;
(c) a molecular weight distribution Mz/Mw of less than 2; and
(d) the presence of two peaks in a TREF measurement.
Particularly preferred VLDPEs having some or all of these characteristics are the gas phase metallocene-produced VLDPEs described above.
Two peaks in the TREF measurement as used in this specification and the appended claims means the presence of two distinct normalized ELS (evaporation mass light scattering) response peaks in a graph of normalized ELS response (vertical or y axis) versus elution temperature (horizontal or x axis with temperature increasing from left to right) using the TREF method disclosed in the EXAMPLES section below. A xe2x80x9cpeakxe2x80x9d in this context means where the general slope of the graph changes from positive to negative with increasing temperature. Between the two peaks is a local minimum in which the general slope of the graph changes from negative to positive with increasing temperature. xe2x80x9cGeneral trendxe2x80x9d of the graph is intended to exclude the multiple local minimums and maximums that can occur in intervals of 2xc2x0 C. or less. Preferably, the two distinct peaks are at least 3xc2x0 C. apart, more preferably at least 4xc2x0 C. apart, even more preferably at least 5xc2x0 C. apart. Additionally, both of the distinct peaks occur at a temperature on the graph above 20xc2x0 C. and below 120xc2x0 C. where the elution temperature is run to 0xc2x0 C. or lower. This limitation avoids confusion with the apparent peak on the graph at low temperature caused by material that remains soluble at the lowest elution temperature. Two peaks on such a graph indicates a bi-modal composition distribution (CD). Bimodal CD may also be determined by other methods known to those skilled in the art. One such alternate method for TREF measurement than can be used if the above method does not show two peaks is disclosed in B. Monrabal, xe2x80x9cCrystallization Analysis Fractionation: A New Technique for the Analysis of Branching Distribution in Polyolefins,xe2x80x9d Journal of Applied Polymer Science, Vol. 52, 491-499 (1994).
A preferred balance of properties, particularly in film applications, according to the invention is achieved when the long chain branching of the VLDPE is reduced. Therefore, with respect to the catalyst structures described above, bis-Cp structures are preferred over mono-Cp structures, unbridged structures are preferred over bridged structures, and unbridged bis-Cp structures are the most preferred. Preferred catalyst systems which will minimize or eliminate long chain branching to produce polymers substantially free of or free of long chain branching are based on un-bridged bis-Cp zirconocenes, such as but not limited to bis (1-methyl-3-n-butyl cyclopentadiane) zirconium dichloride.
Symmetric metallocenes may be used to produce a VLDPE polymer of the present invention. Symmetric metallocenes include, but are not limited to, bis(methylcyclopentadienyl)zirconium dichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, bis(1,2-dimethylcyclopentadienyl)zirconium dichloride, bis(1,2,4-trimethylcyclopentadienyl)zirconium dichloride, bis(1,2,3-trimethylcyclopentadienyl)zirconium dichloride, bis(tetramethylcyclopentadienyl)zirconium dichloride, bis(pentamethylcyclopentadienyl)zirconium dichloride, bis(ethylcyclopentadienyl)zirconium dichloride, bis(propylcyclopentadienyl)zirconium dichloride, bis(butylcyclopentadienyl)zirconium dichloride, bis(isobutylcyclopentadienyl)zirconium dichloride, bis(pentylcyclopentadienyl)zirconium dichloride, bis(isopentylcyclopentadienyl)zirconium dichloride, bis(cyclopentylcyclopentadienyl)zirconium dichloride, bis(phenylcyclopentadienyl)zirconium dichloride, bis(benzylcyclopentadienyl)zirconium dichloride, bis(trimethylsilylmethylcyclopentadienyl)zirconium dichloride, bis(cyclopropylmethylcyclopentadienyl)zirconium dichloride, bis(cyclopentylmethylcyclopentadienyl)zirconium dichloride, bis(cyclohexylmethylcyclopentadienyl)zirconium dichloride, bis(propenylcyclopentadienyl)zirconium dichloride, bis(butenylcyclopentadienyl)zirconium dichloride, bis(1,3-ethylmethylcyclopentadienyl)zirconium dichloride, bis(1,3-propylmethylcyclopentadienyl)zirconium dichloride, bis(1,3-butylmethylcyclopentadienyl)zirconium dichloride, bis(1,3-isopropylmethylcyclopentadienyl)zirconium dichloride, bis(1,3-isobutylmethylcyclopentadienyl)zirconium dichloride, bis(1,3-methylcyclopentylcyclopentadienyl)zirconium dichloride, and bis(1,2,4-dimethylpropylcyclopentadienyl)zirconium dichloride.
Unsymmetric metallocenes may be used to produce a VLDPE polymer of the present invention. Unsymmetric metallocenes include, but are not limited to, cyclopentadienyl(1,3-dimethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(1,2,4-trimethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(tetramethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(pentamethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(propylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(butylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(pentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(isobutylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(cyclopentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(isopentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(benzylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(phenylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(1,3-propylmethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(1,3-butylmethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(1,3-isobutylmethylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(1,2,4-dimethylpropylcyclopentadienyl)zirconium dichloride, (tetramethylcyclopentadienyl)(methylcyclopentadienyl)zirconium dichloride, (tetramethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconium dichloride, (tetramethylcyclopentadienyl)(1,2,4-trimethylcyclopentadienyl)zirconium dichloride, (tetramethylcyclopentadienyl)(propylcyclopentadienyl)zirconium dichloride, (tetramethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconium dichloride, (pentamethylcyclopentadienyl)(methylcyclopentadienyl)zirconium dichloride, (pentamethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconium dichloride, (pentamethylcyclopentadienyl)( greater than 1,2,4-trimethylcyclopentadienyl)zirconium dichloride, (pentamethylcyclopentadienyl)(propylcyclopentadienyl)zirconium dichloride, (pentamethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(ethyltetramentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(propyltetramentylcyclopentadienyl)zirconium dichloride, (methylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium dichloride, (1,3-dimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium dichloride, (1,2,4-trimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium dichloride, (propylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium dichloride, cyclopentadienyl(indenyl)zirconium dichloride, (methylcyclopentadienyl)(indenyl)zirconium dichloride, (1,3-dimethylcyclopentadienyl)(indenyl)zirconium dichloride, (1,2,4-trimethylcyclopentadienyl)(indenyl)zirconium dichloride, (tetramethylcyclopentadienyl)(indenyl)zirconium dichloride, (pentamethylcyclopentadienyl)(indenyl)zirconium dichloride, cyclopentadienyl(1-methylindenyl)zirconium dichloride, cyclopentadienyl(1,3-dimethylindenyl)zirconium dichloride, cyclopentadienyl(1,2,3-trimethylindenyl)zirconium dichloride, cyclopentadienyl(4,7-dimethylindenyl)zirconium dichloride, (tetramethylcyclopentadienyl)(4,7-dimethylindenyl)zirconium dichloride, (pentamethylcyclopentadienyl)(4,7-dimethylindenyl)zirconium dichloride, cyclopentadienyl(5,6-dimethylindenyl)zirconium dichloride, (pentamethylcyclopentadienyl)(5,6-dimethylindenyl)zirconium dichloride, and (tetramethylcyclopentadienyl)(5,6-dimethylindenyl)zirconium dichloride.
The preferred method for producing the catalyst of the invention is described below and can be found in U.S. application Ser. No. 265,533, filed Jun. 24, 1994, now abandoned, and Ser. No. 265,532, filed Jun. 24, 1994, now abandoned, both are hereto fully incorporated by reference in their entirety. In a preferred embodiment, the metallocene catalyst component is typically slurried in a liquid to form a metallocene solution and a separate solution is formed containing an activator and a liquid. The liquid can be any compatible solvent or other liquid capable of forming a solution or the like with at least one metallocene catalyst component and/or at least one activator. In the preferred embodiment the liquid is a cyclic aliphatic or aromatic hydrocarbon, most preferably toluene. The metallocene and activator solutions are preferably mixed together and added to a porous support such that the total volume of the metallocene solution and the activator solution or the metallocene and activator solution is less than four times the pore volume of the porous support, more preferably less than three times, even more preferably less than two times, and more preferably in the 1-1.5 times to 2.5-4 times range and most preferably in the 1.5 to 3 times range. Also, in the preferred embodiment, an antistatic agent is added to the catalyst preparation.
In one embodiment, the metallocene catalyst is prepared from silica dehydrated at 600xc2x0 C. The catalyst is a commercial scale catalyst prepared in a mixing vessel with and agitator. An initial charge of 1156 pounds (462 Kg) toluene is added to the mixer. This was followed by mixing 925 pounds (421 Kg) of 30 percent by weight methyl aluminoxane in toluene. This is followed with 100 pounds (46 Kg) of 20 percent by weight bis(1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride in toluene (20.4 pounds (9.3 Kg) of contained metallocene). An additional 144 pounds (66 Kg) of toluene is added to the mixer to rinse the metallocene feed cylinder and allowed to mix for 30 minutes at ambient conditions. This is followed by 54.3 pounds (25 Kg) of an AS-990 in toluene, surface modifier solution, containing 5.3 pounds (2.4 Kg) of contained AS-990. An additional 100 pounds (46 Kg) of toluene rinsed the surface modifier container and was added to the mixer. The resulting slurry is vacuum dried at 3.2 psia (70.6 kPa) at 175xc2x0 F. (79xc2x0 C.) to a free flowing powder. The final catalyst weight was 1093 pounds (497 Kg). The catalyst can have a final zirconium loading of 0.40% and an aluminum loading of 12.0%.
In one preferred embodiment a substantially homogenous catalyst system is preferred. For the purposes of this patent specification and appended claims, a xe2x80x9csubstantially homogenous catalystxe2x80x9d is one in which the mole ratio of the transition metal of the catalyst component, preferably with an activator, is evenly distributed throughout a porous support.
The procedure for measuring the total pore volume of a porous support is well known in the art. Details of one of these procedures is discussed in Volume 1, Experimental Methods in Catalytic Research (Academic Press, 1968) (specifically see pages 67-96). This preferred procedure involves the use of a classical BET apparatus for nitrogen absorption. Another method well know in the art is described in Innes, Total porosity and Particle Density of Fluid Catalysts By Liquid Titration, Vol. 28, No. 3, Analytical Chemistry 332-334 (March, 1956).
The mole ratio of the metal of the activator component to the transition metal of the metallocene component is in the range of ratios between 0.3:1 to 1000:1, preferably 20:1 to 800:1, and most preferably 50:1 to 500:1. Where the activator is an ionizing activator as previously described the mole ratio of the metal of the activator component to the transition metal component is preferably in the range of ratios between 0.3:1 to 3:1. component to the transition metal component is preferably in the range of ratios between 0.3:1 to 3:1.
Typically in a gas phase polymerization process a continuous cycle is employed where in one part of the cycle of a reactor, a cycling gas stream, otherwise known as a recycle stream or fluidizing medium, is heated in the reactor by the heat of polymerization. This heat is removed in another part of the cycle by a cooling system external to the reactor. (See for example U.S. Pat. Nos. 4,543,399, 4,588,790, 5,028,670, 5,352,749, 5,405,922, 5,436,304, 5,453,471 and 5,462,999 all of which are fully incorporated herein by reference.)
Generally in a gas fluidized bed process for producing polymer from monomers a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and new or fresh monomer is added to replace the polymerized monomer.
In one embodiment of the process of the invention the process is essentially free of a scavenger. For the purposes of this patent specification and appended claims the term xe2x80x9cessentially freexe2x80x9d means that during the process of the invention no more than 10 ppm of a scavenger based on the total weight of the recycle stream is present at any given point in time during the process of the invention.
In another embodiment of the process of the invention the process is substantially free of a scavenger. For the purposes of this patent specification and appended claims the term xe2x80x9csubstantially freexe2x80x9d is defined to be that during the process of the invention no more than 50 ppm of a scavenger based on the total weight of a fluidized bed is present at any given point in time during the process of the invention.
In one embodiment during reactor start-up to remove impurities and ensure polymerization is initiated, a scavenger is present in an amount less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, even more preferably less than 150 ppm, still more preferably less than 100 ppm, and most preferably less than 50 ppm based on the total bed weight of a fluidized bed during the first 12 hours from the time the catalyst is placed into the reactor, preferably up to 6 hours, more preferably less than 3 hours, even more preferably less than 2 hours, and most preferably less than 1 hour and then the introduction of the scavenger is halted.
In another embodiment of the process of the invention the scavenger is present in an amount sufficient until the catalyst of the invention has achieved a catalyst productivity on a weight ratio basis of greater than 1000 grams of polymer per gram of the catalyst, preferably greater than about 1500, more preferably greater than 2000, even more preferably greater than 2500, and most preferably greater than 3000.
In another embodiment of the process of the invention during start-up the scavenger is present in an amount sufficient until the catalyst of the invention has achieved a catalyst productivity 40 percent of that of steady-state, preferably less than 30 percent, even more preferably less than 20 percent and most preferably less than 10 percent. For the purposes of this patent specification and appended claims xe2x80x9csteady statexe2x80x9d is the production rate, weight of polymer being produced per hour.
The productivity of the catalyst or catalyst system is influenced by the main monomer, (i.e., ethylene or propylene) partial pressure. The preferred mole percent of the monomer, ethylene or propylene, is from about 25 to 90 mole percent and the monomer partial pressure is in the range of from about 75 psia (517 kPa) to about 300 psia (2069 kPa), which are typical conditions in a gas phase polymerization process.
When a scavenger is utilized in the process of the invention the scavenger can be introduced typically into the reactor directly or indirectly into the recycle stream or into any external means capable of introducing the scavenger into the reactor. Preferably the scavenger enters into the reactor directly, and most preferably directly into the reactor bed or below the distributor plate in a typical gas phase process, preferably after the bed is in a fluidized state. In one embodiment the scavenger can be introduced once, intermittently or continuously to the reactor system.
The scavenger used in the process of the invention is introduced to the reactor at a rate equivalent to 10 ppm to 100 ppm based on the steady state, production rate, and then scavenger introduction is stopped.
In yet another embodiment particularly during start-up the scavenger when used is introduced at a rate sufficient to provide an increase in catalyst productivity on a weight ratio basis of a rate of 200 grams of polymer per gram of catalyst per minute, preferably at a rate of 300, even more preferably at a rate of 400 and most preferably at a rate of 500.
In another embodiment, the mole ratio of the metal of the scavenger to the transition metal of the metallocene catalyst component equals about, about 0.2 multiplied by the ppm of a scavenger based on the production rate multiplied by the catalyst productivity in kilograms of polymer per gram of catalyst. The range of the mole ratio is from about 300 to 10. In a preferred embodiment, where an alkyl aluminum is used as the scavenger the mole ratio is represented as aluminum (Al) to transition metal, for example, zirconium, where the moles of. Al are based on the total amount of scavenger used.
It is also preferred that hydrogen not be added to the system simultaneously with the scavenger. It is also within the scope of this invention that the scavenger can be introduced on a carrier separate from that used when a supported metallocene catalyst system is used in the process of the invention.
Fines for the purpose of this patent specification and appended claims are polymer particles less than 125 mu in size. Fines of this size can be measured by using a standard 120 mesh unit sieve screen. In a preferred embodiment the amount of scavenger present in the reactor at any given point in time during the process of the invention the level of fines less than 125 mu is less than 10%, preferably less than 1%, more preferably less than 0.85% to less than 0.05%.
It is within the scope of the invention that a system external to the reactor for removing scavengers introduced in the process of the invention from the recycle stream may be used. This would then prevent the recycle of the scavenger back into the reactor and prevent scavenger build-up in the reactor system. It is preferred that such a system is placed prior to the heat exchanger or compressor in the recycle stream line. It is contemplated that such a system would condense the scavenger out of the fluidizing medium in the recycle stream line. It would be preferred that the fluidizing medium is treated to remove the scavenger, see for example U.S. Pat. No. 4,460,755, incorporated herein by reference.
It is also contemplated by the process of the invention that scavenger can be intermittently introduced during the process wherein greater than 90%, preferably greater than 95% of all the scavenger introduced is removed from the recycle stream.
It is also contemplated by this invention that the catalyst or catalyst system or components thereof of the invention can be used upon start-up as a scavenger, however, this would be an expensive procedure.
In the most preferred embodiment of the invention the process is a gas phase polymerization process operating in a condensed mode. For the purposes of this patent specification and appended claims the process of purposefully introducing a recycle stream having a liquid and a gas phase into a reactor such that the weight percent of liquid based on the total weight of the recycle stream is greater than about 2.0 weight percent is defined to be operating a gas phase polymerization process in a xe2x80x9ccondensed modexe2x80x9d.
In one embodiment of the process of the invention the weight percent of liquid in the recycle stream based on the total weight of the recycle stream is in the range of about 2 to about 50 weight percent, preferably greater than 10 weight percent and more preferably greater than 15 weight percent and even more preferably greater than 20 weight percent and most preferably in the range between about 20 and about 40 percent. However, any level of condensed can be used depending on the desired production rate.
In another embodiment of the process of the invention the amount of scavenger utilized if any is used should be in a mole ratio less than 100, preferably less than 50, more preferably less than about 25 based on the mole ratio of the metal of the transition metal scavenger to the transition metal of the metallocene where the scavenger is an aluminum containing organometallic compound and the transition metal of the metallocene is a Group 4 metal then the mole ratio above is based on the moles of aluminum to the moles of the Group 4 metal of the catalyst.
Fouling is a term used to describe the collection of polymer deposits on surfaces in a reactor. Fouling is detrimental to all parts of a polymerization process, including the reactor and its associated systems, hardware, etc. Fouling is especially disruptive in areas restricting gas flow or liquid flow. The two major areas of primary concern are the heat exchanger and distributor plate fouling. The heat exchanger consists of a series of small diameter tubes arranged in a tube bundle. The distributor plate is a solid plate containing numerous small diameter orifices through which the gas contained in a recycle stream is passed through before entering the reaction zone or distributed into a bed of solid polymer in a fluidized bed reactor such as described in U.S. Pat. No. 4,933,149, incorporated herein by reference.
Fouling manifests itself as an increase in the pressure drop across either the plate, cooler, or both. Once the pressure drop becomes too high, gas or liquid can no longer be circulated efficiently by the compressor, and it is often necessary to shut the reactor down. Cleaning out the reactor can take several days and is very time consuming and costly. Fouling can also occur in the recycle gas piping and compressor, but usually accompanies plate and cooler fouling.
To quantify the rate of fouling it is useful to define a fouling factor, F. F is the fraction of the area of a hole that is fouled. If F=0 (0%) then there is no fouling. Conversely, if F=1 (100%) the hole is completely plugged. It is possible to relate the fouling to the pressure drop, DELTA P, at a given time in terms of the pressure drop of a clean system, DELTA P0. As fouling increases DELTA P increases and is larger than the initial pressure drop, DELTA P0. F is given by the following expressions: [See equation in original] (I) Cooler Fouling [See Original Patent for Chemical Structure Diagram] (II) In general, when F is greater than about 0.3 to about 0.4 (30-40%) a reactor shutdown is inevitable. Preferably, F is less than 40%, preferably less than 30%, even more preferably less than 20%, still more preferably less than 15% and most preferably less than 10% to 0%. The rate of fouling, the change in F as a function of time, is used to quantify fouling. If no fouling occurs the rate of fouling is zero. A minimum acceptable rate of fouling for a commercial operation is about 12 percent/month or 0.4 percent/day, preferably less than 0.3 percent/day, even more preferably less than 0.2 percent/day and most preferably less than 0.1 percent/day.
Particle size is determined as follows; the particle size is measured by determining the weight of the material collected on a series of U.S. Standard sieves and determining the weight average particle size.
Fines are defined as the percentage of the total distribution passing through 120 mesh standard sieve.
In one embodiment, the process is operated using a metallocene catalyst based on bis(1,3-methyl-n-butyl cyclopentadienyl) zirconium dichloride is described in this example. It shows the fouling effect of operating a commercial reactor using TEAL. This example includes information from a startup of a commercial reactor on metallocene catalyst.
Possible optimizations of the gas phase polymerization process and additional catalyst preparations are disclosed in U.S. Pat. Nos. 5,763,543, 6,087,291, and 5,712,352, and PCT published applications WO 00/02930 and WO 00/02931.
Although the VLPDE polymer component of the VLDPE/LDPE blends of the invention has been discussed as a single polymer, blends of two or more such VLDPE polymers, preferably two or more m-VLDPE polymers, having the properties described herein are also contemplated.
In any of the gas phase polymerization processes described herein, including those in the patents referenced herein, the unreacted monomers in the product stream may be recycled. Preferably, to make the VLDPEs of the invention with the desired density, the composition of the recycle stream should be carefully controlled so that the proper ratio of comonomers is maintained, as discussed above.
Another aspect of the invention relates to a polymer product containing any one of the very low density polyethylenes (VLDPEs) made using a gas phase polymerization process carried out in the presence of metallocene. Such polymer products preferably contain a sufficient amount of the VLDPE to provide them with improved properties such as the toughness properties described above in the Summary, e.g., the above-mentioned Dart Drop and/or Puncture values. Such products include a number of film-based products, such as films made from the VLDPEs, cast films, melt-blown films, coextruded films, films made of blends of VLDPE together with other polymers, laminated films, extrusion coatings, films with high oxygen transmission rates, multilayer films containing the VLDPEs, sealing layers and cling layers that contain the VLDPEs and products that include such sealing layers and cling layers. The blends of the invention have the VLDPE together with other polymers, such as LDPE, MDPE, HDPE, polypropylene and copolymers such as ethylene/propylene copolymers. This invention also includes products having specific end-uses, particularly film-based products for which the toughness properties are desirable, such as stretch films, shipping sacks, flexible and food packaging (e.g., fresh cut produce packaging), personal care films pouches, medical film products (such as IV bags), diaper backsheets and housewrap. Another product of this invention includes VLDPE that has been rendered breathable and used either alone (as a single layer film) or in combination with one or more other layers or films or fabrics, including woven or nonwoven films or fabrics. The products also include extrusion coating compositions containing the VLDPE. Several specific film and coating applications are described below.
4.2 The LDPE Component
The polymer blend also includes a low density polyethylene (LDPE) polymer. As used herein, the terms xe2x80x9clow density polyethylenexe2x80x9d polymer and xe2x80x9cLDPExe2x80x9d polymer refer to a homopolymer or preferably copolymer of ethylene having a density of from 0.916 to 0.940 g/cm3. Polymers having more than two types of monomers, such as terpolymers, are also included within the term xe2x80x9ccopolymerxe2x80x9d as used herein. The comonomers that are useful in general for making LDPE copolymers include xcex1-olefins, such as C3-C20 xcex1-olefins and preferably C3-C12 xcex1-olefins. The xcex1-olefin comonomer can be linear or branched, and two or more comonomers can be used, if desired. Examples of suitable comonomers include linear C3-C12 xcex1-olefins, and xcex1-olefins having one or more C1-C3 alkyl branches, or an aryl group. Specific examples include propylene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl or propyl sibstituents; 1-hexene with one or more methyl, ethyl or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-octene with one or more methyl, ethyl or propyl substituents; 1 nonene with one or more methyl, ethyl or propyl substituents; ethyl, methyl or dimethyl-substituted 1-decene; 1-dodecene; and styrene. It should be appreciated that the list of comonomers above is merely exemplary, and is not intended to be limiting. Preferred comonomers include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and styrene.
Other useful comonomers include polar vinyl, conjugated and non-conjugated dienes, acetylene and aldehyde monomers, which can be included in minor amounts in terpolymer compositions. Non-conjugated dienes useful as co-monomers preferably are straight chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms. Suitable non-conjugated dienes include, for example: (a) straight chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as 1,4-cyclohexadiene; 15-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene; norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB); 5xe2x80x94propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of the non-conjugated dienes typically used, the preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and tetracyclo-(xcex94-11,12)-5,8-dodecene. Particularly preferred diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB).
The amount of comonomer used will depend upon the desired density of the LDPE polymer and the specific comonomers selected. One skilled in the art can readily determine the appropriate comonomer content appropriate to produce an LDPE polymer having a desired density.
The LDPE polymer has a density of 0.916 g/cm3 to 0.940 g/cm3, and preferably from 0.916 g/cm3 to 0.925 g/cm3. The LDPE polymer can have a melt index of from 0.5 to 20 g/10 min (dg/min), as measured in accordance with ASTM-1238 condition E. Alternative lower limits for the melt index include 0.7 and 1.0 g/10 min, and alternative upper limits for the melt index include 5, 10 and 15 g/10 min, with melt index ranges from any lower limit to any upper limit being within the scope of the invention.
The LDPE polymer can be produced using any conventional polymerization process and suitable catalyst, such as a Ziegler-Natta catalyst or a metallocene catalyst. Metallocene-catalyzed LDPE""s (m-LDPE) are preferred. Particularly preferred m-LDPEs are the gas-phase, metallocene catalyzed LLPDEs described in WO 94/26816, the disclosure of which is incorporated herein by reference for purposes of U.S. patent practice. Examples of suitable LDPEs include the metallocene LDPEs commercially available under the tradename EXCEED(trademark) from ExxonMobil Chemical Co., Houston, Tex., the Ziegler-Natta LDPEs available as ExxonMobil LL series LDPEs, from ExxonMobil Chemical Co., Houston, Tex., and the DOWLEX(trademark) LDPE resins available from Dow Chemical Co.
Although the LLPDE polymer component of the VLDPE/LDPE blends of the invention has been discussed as a single polymer, blends of two or more such LDPE polymers, preferably two or more metallocene-catalyzed LDPE polymers, having the properties described herein are also contemplated.
4.3 VLDPE-LDPE Blends
In one embodiment, the present invention provides a polymer blend, the blend including a VLDPE polymer and an LDPE polymer. The blend can include any of the VLDPE polymers described herein, preferably a metallocene-catalyzed VLDPE polymer, and more preferably a gas-phase produced metallocene catalyzed VLDPE polymer. The blend can include any of the LDPE polymers described herein, preferably a metallocene-catalyzed LDPE polymer, and more preferably a gas-phase produced metallocene catalyzed LDPE polymer.
The blends can be formed using conventional equipment and methods, such a by dry blending the individual components and subsequently melt mixing in a mixer, or by mixing the components together directly in a mixer, such as a Banbury mixer, a Haake mixer, a Brabender internal mixer, or a single or twin-screw extruder including a compounding extruder and a side-arm extruder used directly downstream of a polymerization process. Additionally, additives can be included in the blend, in one or more components of the blend, and/or in a product formed from the blend, such as a film, as desired. Such additives are well known in the art, and can include, for example: fillers; antioxidants (e.g., hindered phenolics such as IRGANOX(trademark) 1010 or IRGANOX(trademark) 1076 available from Ciba-Geigy); phosphites (e.g., IRGAFOS(trademark) 168 available from Ciba-Geigy); anti-cling additives; tackifiers, such as polybutenes, terpene resins, aliphatic and aromatic hydrocarbon resins, alkali metal and glycerol stearates and hydrogenated rosins; UV stabilizers; heat stabilizers; antiblocking agents; release agents; anti-static agents; pigments; colorants; dyes; waxes; silica; fillers; talc and the like.
The blends include at least 1 weight percent and up to 99 weight percent of the VLDPE polymer, and at least 1 weight percent and up to 99 weight percent of the LDPE polymer, with these weight percents based on the total weight of the VLDPE and LDPE polymers of the blend. Alternative lower limits of the VLDPE polymer can be 5%, 10%, 20%, 30% or 40% by weight. Alternative upper limits of the VLDPE polymer can be 95%, 90%, 80%, 70%, and 60% by weight. Ranges from any lower limit to any upper limit are within the scope of the invention. Preferred blends include from 5 to 85%, alternatively from 10-50% or from 10-30% by weight of the VLDPE polymer. The balance of the weight percentage is the weight of the LDPE polymer component.
In one preferred embodiment, the polymer blend includes a metallocene-catalyzed VLDPE polymer having a density of less than 0.916 g/cm3, and an LDPE polymer having a density of from 0.916 to 0.940 g/cm3.
In another preferred embodiment, the polymer blend includes a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and at least one C3 to C12 alpha olefin and having a density of from 0.900 to 0.915 g/cm3 and a melt index of from 0.5 to 20 g/10 min; and a metallocene-produced LDPE polymer, the LDPE polymer being a copolymer of ethylene and at least one C3 to C12 alpha olefin and having a density of from 0.916 to 0.925 g/cm3 and a melt index of from 0.5 to 20 g/10 min, wherein the blend includes 5-85% by weight of the VLDPE polymer and 95-15% by weight of the LDPE polymer, preferably 10-50% by weight of the VLDPE polymer and 90-50% by weight of the LDPE polymer, based on the total weight of the VLDPE and LDPE polymers.
In any of these embodiments, the VLDPE polymer, the LDPE polymer, or both, can be blends of such polymers. I.e., the VLDPE polymer component of the blend can itself be a blend of two or more VLDPE polymers having the characteristics described herein, and alternatively or additionally, the LDPE polymer component of the blend can itself be a blend of two or more LDPE polymers having the characteristics described herein.
4.4 Films, Coatings, and Articles
Films of the metallocene VLDPE polymers of the present invention can be formed by conventional processes, preferably by a chill roll casting process. The polymer is extruded by an extruder, melt processed through a slot die, and melt drawn down by an optional air knife and chill roll. Extrusion coating are generally processed at higher temperatures than cast films, typically about 600xc2x0 F., in order to promote adhesion of the extruded material to the substrate. The resulting polymer film is collected on a winder. The film thickness can be monitored by a gauge monitor, and the film can be edge trimmed by a trimmer. One or more optional treaters can be used to surface treat the film, if desired. Such chill roll casting processes and apparatus are well known in the art, and are described, for example, in The Wiley Encyclopedia of Packaging Technology, Second Edition, A. L. Brody and K. S. Marsh, Ed., John Wiley and Sons, Inc., New York (1997). Other extrusion coating processes are known in the art, and are described, for example, in U.S. Pat. Nos. 5,268,230, 5,178,960 and 5,387,630.
In one embodiment, the present invention is directed to metallocene VLDPE films or coatings of the films on flexible media such as paper, metal foil, polymeric materials such as polypropylene, polyester, and the like. The film resins have a density less than 0.916 g/cm3, and a melt flow ratio (xe2x80x9cMFRxe2x80x9d) of from 6-15 dg/min, preferably of from 9-12 dg/min. In general, the density of the film resin is from 0.890 to 0.915 g/cm3, from 0.905 to 0.915 g/cm3, from 0.910 to 0.915 g/cm3, or from 0.911 to 0.913 g/cm3. In a particular embodiment, the film resin has a density of 0.912 g/cm3 and an MFR of 12 dg/min. These films and coatings can be produced as described above.
It should be emphasized that the VLDPE/LDPE blends of the present invention can make use of VLDPE polymers produced by the methods described herein, or VLDPE polymers produced by other methods known in the art for use in making metallocene VLDPE polymers.
In another embodiment, the present invention is directed to metallocene VLDPE films or coatings of the films on flexible media such as paper, metal foil and the like, wherein the film or coating is formed of a resin including a metallocene VLDPE blended with an LDPE. The substrate can also be stock for milk cartons, juice containers, films, etc. The amount of LDPE in the blend can be from 1 to 40% by weight, preferably from 5 to 35%, from 10 to 30%, or from 15 to 25% by weight. In a particular embodiment, the resin blend includes 20% by weight of an LDPE such as LD200 or LD270, which are commercially available LDPE resins. The resin blends and/or the mVLDPE in the blends, have a density less than 0.916 g/cm3, and a melt flow ratio (xe2x80x9cMFRxe2x80x9d) of from 6-15 dg/min, preferably of from 9-12 dg/min. These films and coatings can be produced as described above. The LDPE and mVLDPE can be blended in conventional processes well known in the art.
The films and coatings of the present invention are also suitable for use in laminate structures; i.e., with a film or a coating as described herein disposed between two substrates. These films and coatings are also suitable for use as heat sealing or moisture barrier layers in single- or multi-layer structures.
Another aspect of the invention relates to the formation of monolayer films from the polymer blend compositions discussed above. These films may be formed by any number of well known extrusion or coextrusion techniques discussed below. Films of the invention may be unoriented, uniaxially oriented or biaxially oriented. Physical properties of the film may vary depending on the film forming techniques used.
Another aspect of the invention relates to the formation of multilayer films from the polymer blend compositions discussed above. Multiple-layer films may be formed by methods well known in the art. The total thickness of multilayer films may vary based upon the application desired. A total film thickness of about 5-100 xcexcm, more typically about 10-50 xcexcm, is suitable for most applications. Those skilled in the art will appreciate that the thickness of individual layers for multilayer films may be adjusted based on desired end use performance, resin or copolymer employed, equipment capability and other factors. The materials forming each layer may be coextruded through a coextrusion feedblock and die assembly to yield a film with two or more layers adhered together but differing in composition. Coextrusion can be adapted for use in both cast film or blown film processes.
When used in multilayer films, the VLDPE/LDPE polymer blend may be used in any layer of the film, or in more than one layer of the film, as desired. When more than one layer of the film is formed of a VLDPE/LDPE polymer blend of the present invention, each such layer can be individually formulated; i.e., the layers formed of the VLDPE/LDPE polymer blend can be the same or different chemical composition, density, melt index, thickness, etc., depending upon the desired properties of the film.
To facilitate discussion of different film structures of the invention, the following notation is used herein. Each layer of a film is denoted xe2x80x9cAxe2x80x9d or xe2x80x9cBxe2x80x9d, where xe2x80x9cAxe2x80x9d indicates a conventional film layer as defined below, and xe2x80x9cBxe2x80x9d indicates a film layer formed of any of the VLDPE polymers of the present invention. Where a film includes more than one A layer or more than one B layer, one or more prime symbols (xe2x80x2, xe2x80x3, xe2x80x2xe2x80x3, etc.) are appended to the A or B symbol to indicate layers of the same type (conventional or inventive) that can be the same or can differ in one or more properties, such as chemical composition, density, melt index, thickness, etc. Finally, the symbols for adjacent layers are separated by a slash (/). Using this notation, a three-layer film having an inner layer of a VLDPE/LDPE polymer blend of the invention disposed between two outer, conventional film layers would be denoted A/B/Axe2x80x2. Similarly, a five-layer film of alternating conventional/inventive layers would be denoted A/B/Axe2x80x2/Bxe2x80x2/Axe2x80x3. Unless otherwise indicated, the left-to-right or right-to-left order of layers does not matter, nor does the order of prime symbols; e.g., an A/B film is equivalent to a B/A film, and an A/Axe2x80x2/B/Axe2x80x3 film is equivalent to an A/B/Axe2x80x2/Axe2x80x3 film, for purposes of the present invention. The relative thickness of each film layer is similarly denoted, with the thickness of each layer relative to a total film thickness of 100 (dimensionless) is indicated numerically and separated by slashes; e.g., the relative thickness of an A/B/Axe2x80x2 film having A and Axe2x80x2 layers of 10 xcexcm each and a B layer of 30 xcexcm is denoted as 20/60/20.
For the various films described herein, the xe2x80x9cAxe2x80x9d layer can be formed of any material known in the art for use in multilayer films or in film-coated products. Thus, for example, the A layer can be formed of a polyethylene homopolymer or copolymer, and the polyethylene can be, for example, a VLDPE, a low density polyethylene (LDPE), an LLDPE, a medium density polyethylene (MDPE), or a high density polyethylene (HDPE), as well as other polyethylenes known in the art. The polyethylene can be produced by any suitable process, including metallocene-catalyzed processes and Ziegler-Natta catalyzed processes. Further, the A layer can be a blend of two or more such polyethylenes, and can include additives known in the art. Further, one skilled in the art will understand that the layers of a multilayer film must have the appropriate viscosity match.
In multilayer structures, one or more A layers can also be an adhesion-promoting tie layer, such as PRIMACOR(trademark) ethylene-acrylic acid copolymers available from The Dow Chemical Co., and/or ethylene-vinyl acetate copolymers. Other materials for A layers can be, for example, foil, nylon, ethylene-vinyl alcohol copolymers, polyvinylidene chloride, polyethylene terephthalate, oriented polypropylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, graft modified polymers, other polyethylenes, such as HDPE, LDPE, LMDPE, and MDPE, and paper.
The xe2x80x9cBxe2x80x9d layer is formed of a VLDPE/LDPE polymer blend of the invention, and can be any of such blends described herein. In one embodiment, the B layer is formed of a blend of a metallocene-catalyzed VLDPE polymer having a density of less than 0.916 g/cm3 and a LDPE polymer having a density of from 0.916 to 0.940 g/cm3. In another embodiment, the B layer is formed of a blend comprising: (a) a gas-phase metallocene-produced VLDPE copolymer of ethylene and at least one C3 to C12 alpha olefin and having a density of from 0.900 to 0.915 g/cm3 and a melt index of from 0.5 to 10 g/10 min; and (b) a LDPE homopolymer or copolymer having a density of from 0.916 to 0.940 g/cm3 and a melt index of from 0.5 to 20 g/10 min. In one embodiment, the B layer is formed of a blend comprising a gas-phase metallocene-produced VLDPE having a melt index having the lower limits of 0.5 g/10 min or more, 0.7 g/10 min or more, 1 g/10 min or more and having the upper limits of 5 g/10 min or less, 3 g/10 min or less, or 2 g/10 min or less, with melt index ranges from any lower limit to any upper limit being within the scope of the invention. In one preferred embodiment, the B layer is formed of a blend as described herein, wherein the VLDPE component of the blend has one or more of the following characteristics, in addition to the density, melt index, and other parameters described herein:
(a) a composition distribution CDBI of 50 to 85%, alternatively 60 to 80%, or 55 to 75%, or 55% or more to 70% or less;
(b) a molecular weight distribution Mw/Mn of 2 to 3, alternatively 2.2 to 2.8;
(c) a molecular weight distribution Mz/Mw of less than 2; and
(d) the presence of two peaks in a TREF measurement.
The thickness of each layer of the film, and of the overall film, is not particularly limited, but is determined according to the desired properties of the film. Typical film layers have a thickness of about 1 to 1000 xcexcm, more typically about 5 to 100 xcexcm, and typical films have an overall thickness of 10 to 100 xcexcm.
In one embodiment, the present invention provides a single-layer (monolayer) film formed of any of the VLDPE/LDPE polymer blends of the invention; i.e., a film having a single layer which is a B layer as described above.
In other embodiments, and using the nomenclature described above, the present invention provides multilayer films with any of the following exemplary structures:
(a) two-layer films, such as A/B and B/Bxe2x80x2;
(b) three-layer films, such as A/B/Axe2x80x2, A/Axe2x80x2/B, B/A/Bxe2x80x2 and B/Bxe2x80x2/Bxe2x80x3;
(c) four-layer films, such as A/Axe2x80x2/Axe2x80x3/B, A/Axe2x80x2/B/Axe2x80x3, A/Axe2x80x2/B/Bxe2x80x2, A/B/Axe2x80x2/Bxe2x80x2, A/B/Bxe2x80x2/Axe2x80x2, B/A/Axe2x80x2/Bxe2x80x2, A/B/Bxe2x80x2/Bxe2x80x3, B/A/Bxe2x80x2/Bxe2x80x3 and B/Bxe2x80x2/Bxe2x80x3/Bxe2x80x2xe2x80x3;
(d) five-layer films, such as A/Axe2x80x2/Axe2x80x3/Axe2x80x2xe2x80x3/B, A/Axe2x80x2/Axe2x80x3/B/Axe2x80x2xe2x80x3, A/Axe2x80x2/B/Axe2x80x3/Axe2x80x2xe2x80x3, A/Axe2x80x2/Axe2x80x3/B/Bxe2x80x2, A/Axe2x80x2/B/Axe2x80x3/Bxe2x80x2, A/Axe2x80x2/B/Bxe2x80x2/Axe2x80x3, A/B/Axe2x80x2/Bxe2x80x2/Axe2x80x3, A/B/Axe2x80x2/Axe2x80x3/B, B/A/Axe2x80x2/Axe2x80x3/Bxe2x80x2, A/Axe2x80x2/B/Bxe2x80x2/Bxe2x80x3, A/B/Axe2x80x2/Bxe2x80x2/Bxe2x80x3, A/B/Bxe2x80x2/Bxe2x80x3/Axe2x80x2, B/A/Axe2x80x2/Bxe2x80x2/Bxe2x80x3, B/A/Bxe2x80x2/Axe2x80x2/Bxe2x80x3, B/A/Bxe2x80x2/Bxe2x80x3/Axe2x80x2, A/B/Bxe2x80x2/Bxe2x80x3/Bxe2x80x2xe2x80x3, B/A/Bxe2x80x2/Bxe2x80x3/Bxe2x80x2xe2x80x3, B/Bxe2x80x2/A/Bxe2x80x3/Bxe2x80x2xe2x80x3, and B/Bxe2x80x2/Bxe2x80x3/Bxe2x80x2xe2x80x3/Bxe2x80x3xe2x80x3;
and similar structures for films having six, seven, eight, nine or more layers. It should be appreciated that films having still more layers can be formed using the VLDPE/LDPE polymer blends of the invention, and such films are within the scope of the invention.
In any of the embodiments above, one or more A layers can be replaced with a substrate layer, such as glass, plastic, paper, metal, etc., or the entire film can be coated or laminated onto a substrate. Thus, although the discussion herein has focussed on multilayer films, the films of the VLDPE/LDPE polymer blends of the present invention can also be used in as coatings; e.g., films formed of the inventive polymers, or multilayer films including one or more layers formed of the inventive polymers, can be coated onto a substrate such as paper, metal, glass, plastic and other materials capable of accepting a coating. Such coated structures are also within the scope of the present invention.
As described below, the films can be cast films or blown films. The films can further be embossed, or produced or processed according to other known film processes. The films can be tailored to specific applications by adjusting the thickness, materials and order of the various layers, as well as the additives in each layer.
In one aspect, films containing the polymer blend composition, monolayer or multilayer, may be formed by using casting techniques, such as a chill roll casting process. For example, a composition can be extruded in a molten state through a flat die and then cooled to form a film. As a specific example, cast films can be prepared using a pilot scale commercial cast film line machine as follows. Pellets of the polymer are melted at a temperature ranging from about 250xc2x0 C. to about 300xc2x0 C., with the specific melt temperature being chosen to match the melt viscosity of the particular resins. In the case of a multilayer cast film, the two or more different melts are conveyed to a coextrusion adapter that combines the two or more melt flows into a multilayer, coextruded structure. This layered flow is distributed through a single manifold film extrusion die to the desired width. The die gap opening is typically about 0.025 inches (about 600 xcexcm). The material is then drawn down to the final gauge. The material draw down ratio is typically about 21:1 for 0.8 mil (20 xcexcm) films. A vacuum box or air knife can be used to pin the melt exiting the die opening to a primary chill roll maintained at about 90xc2x0 F. (32 C). The resulting polymer film is collected on a winder. The film thickness can be monitored by a gauge monitor, and the film can be edge trimmed by a trimmer. One or more optional treaters can be used to surface treat the film, if desired. Such chill roll casting processes and apparatus are well known in the art, and are described, for example, in The Wiley-Encyclopedia of Packaging Technology, Second Edition, A. L. Brody and K. S. Marsh, Ed., John Wiley and Sons, Inc., New York (1997). Although chill roll casting is one example, other forms of casting can be used.
In another aspect, films containing the polymer blend composition, monolayer or multilayer, may be formed using blown techniques, i.e. to form a blown film. For example, the composition can be extruded in a molten state through an annular die and then blown and cooled to form a tubular, blown film, which can then be axially slit and unfolded to form a flat film. As a specific example, blown films can be prepared as follows. The polymer blend composition is introduced into the feed hopper of an extruder, such as a 63.5 mm Egan extruder that is water-cooled, resistance heated, and has an L/D ratio of 24:1. The film can be produced using a 15.24 cm Sano die with a 2.24 mm die gap, along with a Sano dual orifice non-rotating, non-adjustable air ring. The film is extruded through the die into a film that was cooled by blowing air onto the surface of the film. The film is drawn from the die typically forming a cylindrical film that is cooled, collapsed and optionally subjected to a desired auxiliary process, such as slitting, treating, sealing of printing. The finished film can be wound into rolls for later processing, or can be fed into a bag machine and converted into bags. A particular blown film process and apparatus suitable for forming films according to embodiments of the present invention is described in U.S. Pat. No. 5,569,693. Of course, other blown film forming methods can also be used.
In another aspect, the invention relates to any polymer product containing the polymer blend composition produced by methods known in the art. In addition, this invention also includes products having other specific end-uses, such as film-based products, which include stretch films, bags (i.e. shipping sacks, trash bags and liners, industrial liners, and produce bags), flexible and food packaging (e.g., fresh cut produce packaging, frozen food packaging), personal care films pouches, medical film products (such as IV bags), diaper backsheets and housewrap. Products may also include packaging as bundling, packaging and unitizing a variety of products including various foodstuffs, rolls of carpet, liquid containers and various like goods normally containerized and/or palletized for shipping, storage, and/or display. Products may also include surface protection applications, with or without stretching, such as in the temporary protection of surfaces during manufacturing, transportation, etc. There are many potential applications of articles and films produced from the polymer blend compositions described herein.
Alternatively, or additionally, the mVLDPE can be blended with LLDPE, EVA, EMA, either in addition to, or instead of, the LDPE, if desired, in the blends, films, and article described herein.
The advantageous properties described above, as well as others that one skilled in the art will appreciate from the present disclosure, are illustrated herein in the following examples.